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Thousands of police officers from around the region joined the family and friends of slain BART Sgt. Tom Smith, who was killed by friendly fire while searching the one-bedroom apartment of a computer thief suspect. Jodi Hernandez reports. (Published Wednesday, Jan. 29, 2014)

With rain falling from cloudy skies, thousands of police officers from around the region joined the family and friends of slain BART Sgt. Tom Smith, who was killed by friendly fire while searching the one-bedroom apartment of a computer thief suspect.

Early Wednesday morning, firefighters, police officers and politicians began waving flags and saluting a motorcade for Smith, a 42-year-old San Ramon BART detective, who leaves behind a 6-year-old daughter, Summer, and his wife, Kellie, a BART K-9 officer. A row of K-9 officers lined the sidewalk leading up to the church, where his body was taken in a casket, draped with an American flag.

Smith's death on Jan. 21 at a Dublin apartment during a probation search of a suspect who possibly stole a laptop from a BART train, is the first time in the transit agency's history that an officer was killed in the line of duty.

Inside the Neighborhood Church of Castro Valley, Attorney General Kamala Harris told Smith's daughter: "Your dad is a hero."

BART Chief Kenton Rainey said: "It is our challenge to go out and live as Tommy lived. We will never forget."

And outside the church, Palo Alto Police Officer Brad Young said: "When one of us hurts, we all hurt. We are a family."

Smith's family - many in law enforcement like himself - played a role in his service. Pallbearers included his brothers, Alameda County Sheriff's Deputy Ed Smith, Newark Police Officer Patrick Smith, and brother-in-law Todd Shaheen, a Hayward police officer.

What makes Smith's death more painful was that his colleague, Officer Michael Maes, a BART officer of 14 years, accidentally shot him, according to reports in the San Francisco Chronicle. The full report conducted by the Alameda County Sheriff's Office has not yet formally released its conclusion into what happened.

Maes planned to attend Smith's funeral, but it was unclear on Wednesday if he actually came. Many said he did not.

His brother, John Maes, however, spoke to NBC Bay Area on Tuesday, saying his brother was "very sorry and I know he's upset about the whole thing. It's going to be difficult going forward."

He didn't discuss too many details of what might have happened in the apartment that day, saying he has not talked to his brother about the specifics of it.

But John Maes did say that police officers, like anyone, are humans who make mistakes.

The Tommy Smith Memorial fund has been set up at Wells Fargo Bank. Deposits can be made at any Wells Fargo Bank, Account # 5148561086 under Kellie Smith. Or they can be mailed to: Tommy Smith Memorial Fund C/O Wells Fargo, 11020 Bollinger Canyon Road, Suite 1, San Ramon, CA 94582.